Heat a large skillet over medium heat, then add the butter.
Once the butter has melted, add the mushrooms, sauté 5-7 minutes, then add the garlic, sauté 1-2 minutes, then add the spinach and sprinkle the salt and pepper over the top.
Saute for an additional 3-4 minutes, then turn the heat off and set the skillet aside.
Roll the puff pastry sheet out on to a large piece of parchment paper.
If you would like to get fancy with the braided top, follow the next step.If you would like to keep it simple, you can simply wrap the puff pastry around the ingredients without the braid.
To make the braided top, slice a triangle from the bottom of the dough, then slice ½ inch diagonal lines up each side of the pastry.
Place the sauteed mushrooms and spinach in the middle.
Top with the cheese.
If you’re keeping it simple, fold the sides of the puff pastry over.
If you’re using the braid method, lay the rectangular end of the puff pastry over the filling, then begin on one side, and lay one strip of dough over the filling, then alternate laying a strip of dough from the other side, then alternate back and forth, back and forth, over the filling.
Once the entire puff pastry is wrapped up, transfer it on the parchment paper to a baking sheet.
Combine the egg and water to make an egg wash and brush it over the puff pastry.